The present invention is directed to a device for the sequential introduction of plates or sheets into a shaping or forming machine when these sheets are to be introduced one-by-one in succession taken from a bottom of a pile located in a magazine.
Feeding and forming machines include, for example, either printing and grooving machines, or a cut-out machine meant for shaping or forming a sheet made of corrugated cardboard for the preparation of packaging material, which cut-out machine generally comprises tools for printing, for cutting out, and for locally creasing the cardboard so as to form lines for the later folding of the cardboard. In the feeding station for such shaping and forming machines, the plates or sheets contained in a magazine are introduced in succession and in phase with the rotation of the printing and/or cut-out tools.
The precision of the introduction of each plate or sheet into the machine at the suitable time of the cycle enables the correct position for the operations to be performed on the plate, for example the dimension precision of the finished packaging box, as well as the precision and registration of the markings or printings that are to be made on the box blank. That precision is even more important when the cut-out an printed rough packing box must then pass through automatic folding stations, which are now generally the case.
French Patent No. 82 09687 discloses one example of an introduction device used in the usual machine. The introduction device includes means to move along, in a synchronized manner, sheets of corrugated cardboard, which means includes endless belts that rotate intermittently in a single direction and are brought against a lower sheet of a pile by a lifting member that works against an upper run of each of the endless belts. The forward motion of the endless belts and the lifting members are actuated in a manner so that the sheet will be moved along in synchronism with a machine for the subsequent treatment of the sheet. To maintain the sheet against the belts, a continuous vacuum is used. This makes it possible to prevent a sliding that normally is associated with the use of belts rotating in a continuous manner with the application of an intermittent suction pressure. The device, furthermore, is associated with a mechanism that makes it possible to stop, one time out of two, the moving of the sheets.
Another device for the introduction of sheets is described in U.S. Pat. No. 4,614,335. This device relates to a feeding attachment in which there is used a series of small discs or rollers placed into rotation, always in the same direction, and means which will accelerate and retard the speed of rotation of the small discs or rollers. These small rollers are mounted in an upper closing plate of a vacuum chamber that is vertically movable under the action of a cam and lever arrangement. Thus, the departure of the sheet is insured by removing the lower sheet of a pile from the driving small discs or rollers by a raising motion of the vacuum chamber. The same device, in a special form of execution, is described in U.S. Pat. No. 4,681,311, which is a continuation of the first-mentioned U.S. Patent and includes feeding rollers or belts that introduce the sheet between the introduction rollers without any sliding.
A third device that constitutes a variation of the above-mentioned processes and devices is described in detail in European Patent Application published under number 01 83 361. This third device has introducing members which are formed by small discs or rollers coated with a material having a high friction coefficient and which rollers cooperate with a member that lifts the pile of sheets. The small discs or rollers are placed in an enclosure formed by a vacuum chamber. The small discs or rollers are governed in a manner such that they can be driven in two directions of rotation so as to free the pile of sheets from the front gate member, which is arranged so that only one sheet passes at a time between the lower edge of the gate member and a surface, which is defined by the plane of the introduction table and constitutes one of the upper walls of the vacuum chamber.
The above-described three devices have a major drawback with respect to replacement of the introduction members in contact with the sheet to be introduced. Indeed these members are subjected to great wear and require frequent replacement. The replacement causes an important down-time for the machine because the introduction members are arranged in such a manner that a complete disassembly of the introduction station often is necessary in order to make the necessary replacements and repairs. Besides, in all of the devices that make use of small discs or rollers as introduction members, it is necessary to change some of them more frequently, because of the uneven wear that may be present because of their relative position to the various formats of the sheets being handled. Other drawbacks, and not among the least ones, results from the fact that the suction chamber is a single chamber and acts over the entire plane defined by the lower sheet of the pile. Thus, during the work with different size sheet formats, there occurs losses of vacuum that may bear a negative influence on the good functioning of the device.
A drawback particular to the first device of the above-mentioned devices is the fact that the members for the lifting of the endless belt is formed by an articulated shoe which has a vertical movement that alternates from the bottom up and from the top down. The endless belts move linearly in a direction toward the front gate to insure the introduction of the sheet, and of necessity a friction will occur between the upper run and the support surface of the lifting member during the introduction of a sheet. With time, this friction causes the wearing out of an internal face of the belt, which will be subjected to wear stresses on its external faces in contact with the sheet, as well as on the internal face meant to insure the adhesion of the endless belt around the driving and return pulleys. This arrangement, of course, will have an important effect on the life span of the endless belt and will require, therefore, frequent replacement of the introducing members which, as mentioned above, causes an immobilizing of the machine over a period of time corresponding to the time necessary for the disassembly of the introduction station. The time for the replacement of the introduction member being important, there will follow, of course, an important decrease in the total efficiency of the machine.